Macro for multiple-value when definitions

The two macros below introduce new syntax for adding definitions to more than one 'when' determinant value at the same time. The first macro overloads 'extend' keyword and the second is the equivalent for 'when' keyword.

A use example:

extend [HUGE, BIG] packet {
    // definitions that pertain to these subtypes
};

The above code would be expanded in the following (naive) way:

extend HUGE packet {
    // definitions that pertain to these subtypes
};
extend BIG packet {
    // definitions that pertain to these subtypes
};


The macros code:

define 'statement>
       "extend \['name>,...\] 'name> ({;...})" as computed {
    for each in 'names> do {
        result = appendf("%sextend %s %s %s;",result,it,'name>,);
    };
    result = appendf("{%s}",result); // required only for versions 6.1.1 or earlier
};

define 'struct_member>
       "when \['name>,...\] 'name> ({;...})" as computed {
    for each in 'names> do {
        result = appendf("%swhen %s %s %s;",result,it,'name>,);
    };
    result = appendf("{%s}",result); // required only for versions 6.1.1 or earlier
};